Lash adjuster assemblies for use in preventing back-lash in a valve member drive train driven by a rotary cam of an internal combustion engine have been known for many years. Such assemblies generally feature a plunger member that is operably connected to the valve member drive train and moveably disposed within an open-ended bore of body member mounted on the engine which, by means of reciprocating movement, is operable to cyclically pressurize fluid sych as engine oil to provide a pressurized fluid interface within the drive train operable to prevent back lash in the components of the drive train operably connecting the cam member to the valve member. The reciprocating action of the plunger member is generally initiated for a first type of installation where the rotary cam member driven by the engine is operatively engaged with the plunger member through a suitable drive train such as a pivoted rocker arm or the like while the body member is disposed within a closed bottom bore in the engine block and a second type where the body member is moveable reciprocally within an open-ended bore within an engine block where the body member itself is reciprocated by direct engagement with the rotating cam member.
The lash adjuster assemblies in both types of installations employ a retainer member (commonly called a cap retainer) secured to the body member and adapted to hold the plunger member within the body member bore without interfering with the reciprocating movement of the plunger member relative thereto.
The retainer member operates to contain the plunger member within the body member after assembly and prior to installation with a valve member drive train of an internal combustion engine. Typical body member retainer members are formed of stamped metal and have a central opening positioned over the open end of the body member in register with the plunger member. The plunger member is commonly provided with a shoulder adapted to abut the retainer member to limit its movement away from the body member to within a prescribed distance and to hold the plunger member to the body member during operation of the assembly. The body member will typically include a groove on the exterior thereof and an overlying portion of the retainer member is permanently plastically deformed for retention therewith.
An alternative approach has been the use of a snap or split ring action retainer member which embraces the outer body member surface.
Although widely commerically practiced, these approaches have a number of shortcomings. The metal retainers must be permanently deformed during assembly, a process requiring special tooling and process control to maintain acceptable tolerances. This form of mechanical attachment produces only point contact between the retainer member and the body member whereby the retaining forces are unequally distributed about the body member. Such unequal force distribution can distort the body, imparing plunger movement and interfit within the mating head bore. Because assembly is typically affected at room temperature, the clamping forces can be lost or very substantially reduced at elevated temperatures found during normal engine operating conditions whereby the retainer member can release from the body member and interfere with valve train operation. Split ring type retainers likewise apply uneven clamping forces and are prone to fatigue and early catastrophic failure. A further disadvantage of the deformed metal type retainer members is evident in lash adjuster assembly designs employing a bulbous or enlarged end portion of the plunger member which abuts a rocker arm to reduce per unit surface loading. The deformed metal approach is wholly unacceptable for this application, leaving only the split ring approach with its above-mentioned shortcomings. A further disadvantage of prior art metal retainer members arises from their physical size and the difficulty of adequately identifying a retainer member prior to assembly in a lash adjuster assembly. As is often the case, a manufacturer may produce many variations of a particular lash adjuster assembly, the retainer members of each which may be dimensionally distinct but visually indistinguishable. Problems arising from confusion of the identity of parts and misassembly is self-evident. An even further disadvantage of such prior art retainer members is that they characteristically provide a clearance about the plunger member through which fluid is liable to escape from the assembly.
Further, once assembled, it has heretofore been necessary to remove the retainer member from the body member before the plunger member could be removed for replacement or repair due to the underlying presence of the plunger member shoulder beneath the retainer member.
In view of the above, a need exists to provide an improved lash adjuster assembly employing a cap retainer member secured to a body member of the assembly and operative to retain movement of a reciprocating plunger member moveably disposed within a bore of a body member of the assembly to within a prescribed distance and to hold the plunger to the body member while enabling the plunger member to be removed from the body member bore without releasing the retainer member from the body member in addition to providing a fluid seal between the plunger member and the body member bore able to effectively reduce loss of fluid from the assembly.